But soil labs that farmers contract with do not always give accurate
nitrogen fertilizer recommendations; they generally measure only the amount of
inorganic nitrogen in the soil samples that farmers provide. There isn't a good
mechanism for the labs to use to factor in the amount of nitrogen that is
released naturally by microbial degradationnitrogen
mineralizationwhen soilborne bacteria chew up organic matter such as
residues left from the previous crop.

But that may change, now that Agricultural Research Service scientists have
found a way to more accurately assess microbial breakdown of straw and stalks.
The new method cuts in half the error between measured and predicted nitrogen
mineralization rates.

"Using more accurate nitrogen fertilization recommendations will help
farmers nationwide, and it could reduce nitrogen fertilizer costs by $10 to $30
per acre," says Merle F. Vigil, an ARS soil scientist at the Central Great
Plains Research Station in Akron, Colorado. "'And more accurate rates will
help reduce the environmental threat of excess nitrogen seeping downward toward
water supplies."

The new technique uses computers to predict the effect of temperature on
mineralization rates in soils.

The scientists collected data from soils mixed with different crop residues.
They took measurements for up to 160 days at four temperatures ranging from
40° F to 90° F.

They plugged that data into a computer model called MINIMOfor
Mineralization and Immobilizationthat was originally developed by
scientists in Israel, The Netherlands, and the United States. It is a
subroutine of CERES-Maize, developed by ARS, Texas A&M, and Michigan State
University scientists.

"The technique will be of more benefit to farmers in the East and
Midwestwhere soils contain more native organic matterthan in the
more arid areas of the western United States," says Vigil.

Vigil is now working on ways to help soil-testing labs give more accurate
assessments of how much cattle and swine manure, plowed-under green crops like
rye and alfalfa, or sewage sludge help meet crop fertilizer requirements and
reduce the need for commercial sources. -- By Dennis Senft, ARS.